How to cover the entire 100 milliseconds without ion excitation?

When applying the Stored-waveform Inverse Fourier Transform (SWIFT) waveform into an ion trap within the notches, the ion motion is observed on the output plot. Initially, the motion is visible from 0 to 30 milliseconds without any excitation, but the subsequent 70 milliseconds do not appear on the plot. I aim to modify this portion of the code to visualize the entire 100 milliseconds without any excitation. How can I achieve this? Thanks.

%swift

swift_value=swift_amp*swift_total(swift_count)/2/r0;

if swift_count>30000&&swift_count<70000

swift_value=30000*swift_amp*swift_total(swift_count)/2/r0;

else

swift_value=swift_amp*swift_total(swift_count)/2/r0;

end

E_swift=swift_value;

Eac=E_swift;

Answer 1

[Akanksha]

Hey Surik Ahmed,

The issue with your provided code seems to be related to how the excitation signal (swift_value) is being modified between 30 ms and 70 ms. Herein the code multiplies the excitation by 30,000, which is likely too large and may be causing numerical instability or suppressing the ion motion.

To visualize the full 100 ms without any excitation, you should remove or bypass the conditional block and set the excitation to zero.

Kindly go through the following updated code that I have tried enclosed with the output:

% Parameters 
total_time_ms = 100;           % Total simulation time in milliseconds 
sampling_rate = 1e6;           % 1 MHz sampling rate (1 µs per sample) 
total_samples = total_time_ms * 1e3;  % Total number of samples 

% Ion trap parameters (example values) 
r0 = 1;                        % Characteristic dimension of the trap 
swift_amp = 1;                 % Amplitude of SWIFT waveform 
swift_total = randn(1, total_samples);  % Simulated SWIFT waveform (random noise) 

% Initialize arrays 
Eac = zeros(1, total_samples);  % No excitation 
ion_motion = zeros(1, total_samples);  % Placeholder for ion motion 

% Simulate ion motion (example: simple harmonic motion without excitation) 
for swift_count = 1:total_samples 
    % No excitation applied 
    swift_value = 0; 
    E_swift = swift_value; 
    Eac(swift_count) = E_swift; 
    
    % Simulated ion motion (e.g., natural oscillation) 
    ion_motion(swift_count) = sin(2 * pi * 1000 * swift_count / sampling_rate);  % 1 kHz natural frequency 
end 

% Time axis in milliseconds 
time_ms = (0:total_samples - 1) / 1000; 

% Downsample for smoother plotting (e.g., every 100th point) 
downsample_factor = 100; 
time_ds = time_ms(1:downsample_factor:end); 
motion_ds = ion_motion(1:downsample_factor:end); 

% Plot the ion motion 
figure; 
plot(time_ds, motion_ds, 'r'); 
xlabel('Time (ms)'); 
ylabel('Ion Motion (arb. units)'); 
title('Ion Motion Without Excitation (0–100 ms)'); 
grid on; 

Hope this helps!